T-shaped gate and method for improving the edge profile of the gate cap of a t-shaped gate

Abstract

The present application relates to a kind of T-shaped gate and the method for improving the bottom edge shape of T-shaped gate cap, belong to the technical field of semiconductor material, for solving the problem that thin film layer can cause the " umbrella-like " overflow of cap bottom edge profile in prior art, further affect the stability of device.The present application discloses a kind of method for improving the bottom edge shape of T-shaped gate cap, the method includes the preparation of first photoresist layer / thin film layer / third photoresist layer three-layer glue structure, the material of the thin film layer is Al2O3.The method of the present application selects Al2O3 as the thin film layer of intermediate layer in the double-layer glue uniform coating process of T-gate device, reduces the too fast drilling of thin film layer metal when upper photoresist is developed, inhibits the phenomenon of expansion on both sides of corrosion area, optimizes the steepness of T-gate device structure cap metal edge, improves the stability of T-shaped gate morphology process, thereby improves the stability of T-shaped gate process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor materials, and particularly relates to a T-shaped gate and a method for improving the bottom edge morphology of a T-shaped gate cap. BACKGROUND

[0002] Modern wireless communication networks have become the foundation of a country's economic development and international competitiveness, and have become an indispensable part of human society. With the rapid development of high-bandwidth information industries, there is also a demand for high-speed transmission in the military field, such as radar, base station construction, etc., which brings greater challenges to global mobile data transmission. In order to meet the requirements of future mobile communications such as 5G / 6G, the performance improvement of microwave and millimeter wave devices is imminent.

[0003] The third generation of semiconductors represented by GaN materials has a wide band gap, strong polarization effect, high 2DEG concentration, high breakdown field strength, high thermal conductivity, stable chemical properties, high electron saturation drift rate, etc., compared with the first and second generations of semiconductors represented by Si and GaAs. It is an ideal material for manufacturing high-temperature, high-frequency, high-power microwave and millimeter wave devices.

[0004] The HEMT device with high-concentration 2DEG at the heterojunction by utilizing the polarization effect between different materials (such as AlGaN / GaN) is a commonly used structure. Its working principle: a gate metal is placed above the formed 2DEG channel, i.e. between the source and the drain, to form a Schottky contact, and the electron concentration under the gate is controlled by applying different voltages to the gate. When the external voltage is less than the opening voltage, the electrons in the channel are depleted, and the device is turned off; when the external gate voltage is greater than the opening voltage, the electrons in the channel are not depleted, and the device is turned on. The introduction of the gate electrode directly affects the frequency performance of the device due to its own resistance and capacitance characteristics. In order to improve the performance of the device, optimization of the gate electrode is essential. The T-shaped gate structure is commonly used in microwave and radio frequency devices and circuits, and the consistency of the gate cap morphology and profile of the T-shaped gate largely determines the consistency of the device and the circuit, so process control of the T-shaped gate morphology is very critical.

[0005] In the traditional fabrication process of T-shaped gate, a three-layer resist structure of "first photoresist layer / thin film layer / third photoresist layer" is usually used. After electron beam exposure and development, the shape and position of the T-shaped gate basic structure are formed. Then, the gate metal is deposited on the developed substrate, and the T-shaped gate structure is obtained through standard stripping process. The common thin film layers include PMGI, Al or PMMA, etc. If PMGI or PMMA is used, a certain thickness needs to be uniformly coated, and the three-layer resist structure may be mutually soluble, which leads to uncontrollable development process and uncontrollable photoresist shape, resulting in serious overhanging of the edge profile of the cap metal of the T-shaped gate. The process is unstable, which affects the stability of the small-pitch device. The use of Al as the thin film layer can solve the mutual solubility of the photoresist, but Al is active due to its metallic property, which may react with the upper layer of resist during development, resulting in etching and "umbrella-shaped" overhanging of the edge profile of the cap metal of the T-shaped gate. SUMMARY

[0006] In view of the above analysis, the present application aims to provide a T-shaped gate and a method for improving the edge profile of the cap of the T-shaped gate, so as to solve the problem that the thin film layer may cause the edge profile of the cap of the T-shaped gate to appear "umbrella-shaped" overhanging, thereby affecting the stability of the device.

[0007] In a first aspect, the present application provides a method for improving the edge profile of the cap of the T-shaped gate, which comprises the preparation of a three-layer resist structure of "first photoresist layer / thin film layer / third photoresist layer", and the material of the thin film layer is Al2O3.

[0008] Preferably, the Al2O3 thin film layer is prepared by electron beam evaporation or magnetron sputtering method.

[0009] Preferably, the electron beam evaporation specifically comprises: forming an aluminum metal film layer by electron beam evaporation under vacuum conditions, and introducing oxygen to form an Al2O3 thin film layer.

[0010] Preferably, the magnetron sputtering method specifically comprises: forming an Al2O3 thin film layer by magnetron sputtering with the introduction of argon and oxygen.

[0011] Preferably, the method specifically comprises the following steps:

[0012] (1) uniformly coating a first photoresist on a substrate to form a first photoresist layer;

[0013] (2) preparing a thin film layer on the first photoresist layer, and the material of the thin film layer is Al2O3;

[0014] (3) uniformly coating a third photoresist on the Al2O3 thin film layer to form a three-layer resist structure of "first photoresist layer / thin film layer / third photoresist layer";

[0015] (4) electron beam exposure and development on the first photoresist layer / thin film layer / third photoresist layer three-layer glue structure, to form the shape and position of the T-gate basic structure after development, to obtain the developed substrate;

[0016] (5) preparing a gate metal layer on the developed substrate;

[0017] (6) removing the gate metal layer outside the T-gate basic structure shape and position and the first photoresist layer / thin film layer / third photoresist layer three-layer glue structure remaining after development, to obtain an improved T-gate.

[0018] Preferably, in step (1), the first photoresist is PMMA or ZEP.

[0019] Preferably, in step (2), the thickness of the Al2O3 thin film layer is 0.5-100 nm.

[0020] Preferably, in step (3), the third photoresist is ZEP, UVIII or PMMA.

[0021] Preferably, in step (4), the lower surface of the cap of the T-gate pattern is flush with the lower surface of the thin film layer, and the lower surface of the foot of the T-gate pattern is flush with the lower surface of the first photoresist layer.

[0022] In a second aspect, the application provides a T-gate prepared by the method.

[0023] Compared with the prior art, the application can achieve at least one of the following beneficial effects:

[0024] (1) The method of the application selects an Al2O3 thin film layer as the thin film layer in the intermediate layer of the double-layer glue uniform coating process of the T-gate device, which reduces the too fast etching of the metal of the thin film layer during the development of the upper photoresist, inhibits the phenomenon of lateral expansion of the corrosion area, optimizes the steepness of the edge of the cap metal of the T-gate device structure, improves the stability of the T-gate morphology process, and thus improves the stability of the T-gate process.

[0025] (2) The method of the application is not limited to the preparation of AlGaN / GaN microwave or millimeter wave devices, but can also be used for the preparation of gate structures of GaAs, InP and other related microwave devices.

[0026] The above technical solutions can be combined with each other in the application to achieve more preferred combination solutions. Other features and advantages of the application will be described in the subsequent specification, and some advantages will become apparent from the specification or be understood by implementing the application. The purpose and other advantages of the application can be achieved and obtained from the specific contents indicated in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 A process flow diagram for improving the bottom edge morphology of a T-shaped grid cap is provided for this invention;

[0029] Figure 2 This is a schematic diagram of the structure of a T-shaped gate in the prior art;

[0030] Figure 3 SEM image of the T-shaped gate prepared by the method of the present invention;

[0031] Figure 4 SEM image of the T-shaped gate sidewall prepared by the method of the present invention;

[0032] Figure 5a Microscopic images of T-shaped grids in the prior art;

[0033] Figure 5b Microscopic images of the T-shaped grid prepared by the method of the present invention;

[0034] Figure 6a Scanning electron microscope images of T-shaped grids in the prior art;

[0035] Figure 6b Scanning electron microscope (SEM) image of the T-shaped grid prepared by the method of the present invention.

[0036] Figure label:

[0037] 1-Substrate, 2-First photolithography layer, 3-Thin film layer, 4-Third photolithography layer, 5-Gate metal layer, 6-T-gate. Detailed Implementation

[0038] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0039] In the traditional manufacturing process of T-gates, a three-layer photoresist structure consisting of a first photolithography layer, a thin film layer, and a third photolithography layer is commonly used. Electron beam exposure and development are performed on the three-layer photoresist structure to form the shape and position of the basic T-gate structure. On the developed substrate, gate metal is deposited, and the T-gate structure is obtained through a standard stripping process.

[0040] The T-shaped grid described in this invention has a T-shaped cross-section. The vertical portion of the T-shaped grid is the grid foot, and the horizontal portion is the grid cap.

[0041] A specific embodiment of the present invention discloses a method for improving the bottom edge morphology of a T-shaped gate cap. The method includes the preparation of a three-layer adhesive structure consisting of a first photolithography layer 2, a thin film layer 3, and a third photolithography layer 4, wherein the material of the thin film layer 3 is Al2O3.

[0042] It should be noted that the structural diagram of the T-shaped gate in the prior art is as follows: Figure 2 As shown, the microscope image is as follows Figure 5a As shown, the scanning electron microscope image is as follows: Figure 6a As shown.

[0043] In existing technologies, the thin film layer 3 is typically made of PMGI, Al, or PMMA. Using PMGI or PMMA requires uniform coating to a certain thickness, and the three layers of photoresist exhibit mutual solubility, leading to uncontrollable development and uncontrollable photoresist morphology. This results in severe protrusion of the metal edge contour of the T-gate 6 gate cap, causing process instability and affecting the stability of small-pitch devices. While using Al as the thin film layer can solve this photoresist mutual solubility problem, Al's reactive nature causes it to react during the development of the upper photoresist layer, resulting in etching. Simultaneously, an "umbrella-shaped" overflow (e.g., ...) appears at the bottom of the T-gate 6 gate cap. Figure 2 (As shown).

[0044] This leads to easy contact between the T-shaped gate 6 and the drain-source edges, causing a short circuit. This limits the process requirements for further reducing the drain-source spacing, resulting in uncontrollable processes and affecting the stability of small-pitch devices. Using Al metal as the thin film layer 3 can solve the photoresist miscibility problem, but due to the reactive nature of Al metal, it will react during the development of the upper resist layer, causing etching. At the same time, a "umbrella-shaped" overflow phenomenon will also occur at the bottom edge of the gate cap metal.

[0045] The method of the present invention selects the thin film layer 3 as an Al2O3 thin film layer, which reduces the excessively rapid etching of the metal of the thin film layer 3 during the development of the upper photoresist, suppresses the phenomenon of outward expansion on both sides of the etched area, optimizes the steepness of the metal edge of the gate cap of the T-gate device structure, improves the stability of the T-gate 6 morphology process, and thus improves the stability of the T-gate 6 process.

[0046] In one specific embodiment, the Al2O3 thin film layer is prepared by electron beam evaporation or magnetron sputtering.

[0047] In one specific embodiment, the electron beam evaporation specifically includes: forming an Al metal film layer by electron beam evaporation under vacuum conditions, followed by full oxidation by introducing oxygen for 10-1800s to form an Al2O3 thin film layer.

[0048] In one specific implementation, an Al metal film with a thickness of 0.5 nm is formed by electron beam evaporation.

[0049] In one specific implementation, an Al metal film with a thickness of 50 nm is formed by electron beam evaporation.

[0050] In one specific implementation, an Al metal film with a thickness of 100 nm is formed by electron beam evaporation.

[0051] In one specific embodiment, oxygen is introduced for 10 seconds to fully oxidize the material and form an Al2O3 thin film layer.

[0052] In one specific embodiment, oxygen is introduced for 900 seconds to fully oxidize the material, forming an Al2O3 thin film layer.

[0053] In one specific embodiment, oxygen is introduced for 1800 seconds to fully oxidize the material, forming an Al2O3 thin film layer.

[0054] It should be noted that the electron beam evaporation conditions are: a background vacuum of 8 × 10⁻⁶. -6 mbar, evaporation power is 100-3000w.

[0055] In one specific embodiment, the electron beam evaporation conditions are: a background vacuum of 8 × 10⁻⁶. -6 mbar, evaporation power is 100w.

[0056] In one specific embodiment, the electron beam evaporation conditions are: a background vacuum of 8 × 10⁻⁶. -6 mbar, evaporation power is 1500w.

[0057] In one specific embodiment, the electron beam evaporation conditions are: a background vacuum of 8 × 10⁻⁶. -6 mbar, evaporation power is 3000w.

[0058] In one specific embodiment, the magnetron sputtering method specifically includes: using magnetron sputtering to introduce argon and oxygen gas to form an Al2O3 thin film layer.

[0059] It should be noted that the magnetron sputtering conditions are: a background vacuum of 5 × 10⁻⁶. -6 mbar, sputtering power of 100-3000w, and gas is a mixture of argon and oxygen.

[0060] In one specific implementation, the magnetron sputtering conditions are: a base vacuum of 5 × 10⁻⁶. -6 mbar, sputtering power of 100w, gas is a mixture of argon and oxygen.

[0061] In one specific implementation, the magnetron sputtering conditions are: a base vacuum of 5 × 10⁻⁶. -6mbar, sputtering power of 1500w, gas is a mixture of argon and oxygen.

[0062] In one specific implementation, the magnetron sputtering conditions are: a base vacuum of 5 × 10⁻⁶. -6 mbar, sputtering power of 3000w, gas is a mixture of argon and oxygen.

[0063] In one specific embodiment, the method for improving the bottom edge morphology of the T-shaped gate cap includes the following steps, as shown in the process flow diagram. Figure 1 As shown:

[0064] (1) A first photoresist is uniformly coated on the substrate 1 to form a first photolithography layer 2;

[0065] (2) A thin film layer 3 is prepared on the first photolithography layer 2, wherein the material of the thin film layer 3 is Al2O3;

[0066] (3) A third photoresist is uniformly coated on the Al2O3 thin film layer to form a three-layer photoresist structure of first photoresist layer 2 / thin film layer 3 / third photoresist layer 4.

[0067] (4) Electron beam exposure and development are performed on the three-layer photoresist structure of the first photolithography layer 2 / thin film layer 3 / third photolithography layer 4. After development, the shape and position of the T-shaped grid base structure are formed, and the developed substrate is obtained.

[0068] (5) Prepare a gate metal layer on the developed substrate;

[0069] (6) Remove the gate metal layer outside the shape and position of the T-type gate base structure and the three-layer adhesive structure of the first photolithography layer 2 / thin film layer 3 / third photolithography layer 4 remaining after development to obtain the improved T-type gate.

[0070] In one specific implementation, in step (1), the first photoresist is PMMA or ZEP.

[0071] In one specific implementation, in step (1), the first photoresist is PMMA.

[0072] In one specific implementation, in step (1), the first photoresist is ZEP.

[0073] It should be noted that in step (1), substrate 1 is an epitaxial layer deposited on a substrate;

[0074] The substrate can be GaAs, SiC, Sapphire, GaN, or other planar substrate materials. For example, AlN, GaN, and AlGaN can be deposited sequentially on the substrate.

[0075] The substrates 1 used in this invention are all prepared using existing technologies, and will not be explained in detail here.

[0076] The substrate 1 in this invention is illustrated by taking the sequential deposition of AlN, GaN and AlGaN on a SiC substrate as an example, but it is not limited to this.

[0077] In one specific implementation, in step (2), the thickness of the Al2O3 thin film layer is 0.5-100 nm.

[0078] In one specific implementation, in step (2), the thickness of the Al2O3 thin film layer is 0.5 nm.

[0079] In one specific implementation, in step (2), the thickness of the Al2O3 thin film layer is 50 nm.

[0080] In one specific implementation, in step (2), the thickness of the Al2O3 thin film layer is 100 nm.

[0081] In one specific implementation, in step (3), the third photoresist is ZEP, UVIII, or PMMA.

[0082] In one specific implementation, in step (3), the third photoresist is ZEP.

[0083] In one specific implementation, in step (3), the third photoresist is UVIII.

[0084] In one specific implementation, in step (3), the third photoresist is PMMA.

[0085] In one specific implementation, in step (4), the lower surface of the gate cap in the T-shaped gate pattern is flush with the lower surface of the thin film layer 3, and the lower surface of the gate foot in the T-shaped gate pattern is flush with the lower surface of the first photolithography layer 2.

[0086] Specifically, in step (5), the material of the gate metal layer 5 is at least one of Ni, Au, Cu and Ag.

[0087] It should be noted that the gate feet in the T-shaped gate pattern are completely filled with gate metal, and the thickness of the gate cap of the T-shaped gate is less than the total thickness of the thin film layer 3 and the third photolithography layer 4.

[0088] Another embodiment of the present invention discloses a T-shaped gate prepared by the method.

[0089] The SEM images of the T-shaped gate and sidewalls prepared in this embodiment are as follows: Figures 3-4 As shown, the microscope image is as follows Figure 5b As shown, the scanning electron microscope image is as follows: Figure 6bAs shown.

[0090] As can be seen from the figure, the T-gate cap prepared by the method of the present invention has a flat edge, which reduces the excessively rapid etching of the metal of the thin film layer 3 during the development of the upper photoresist, suppresses the phenomenon of outward expansion of the etched area on both sides, optimizes the steepness of the metal edge of the gate cap of the T-gate device structure, improves the stability of the T-gate morphology process, and thus improves the stability of the T-gate process.

[0091] Compared with the prior art, the method of the present invention selects the thin film layer of Al2O3 as the intermediate layer in the double-layer photoresist coating process of T-gate device, which reduces the excessively rapid etching of the thin film metal during the development of the upper photoresist, suppresses the phenomenon of outward expansion of the etched area on both sides, optimizes the steepness of the metal edge of the gate cap of T-gate device structure, improves the stability of T-gate morphology process, and thus improves the stability of T-gate process.

[0092] The method of this invention is not limited to the fabrication of AlGaN / GaN microwave or millimeter-wave devices, but can also be used for the fabrication of gate structures for related microwave devices such as GaAs and InP.

[0093] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the bottom edge morphology of a T-shaped grid cap, characterized in that, The method includes the preparation of a three-layer adhesive structure consisting of a first photolithography layer, a thin film layer, and a third photolithography layer, wherein the material of the thin film layer is Al2O3; The method specifically includes the following steps: (1) A first photoresist is uniformly coated on the substrate to form a first photolithography layer, wherein the first photoresist is PMMA or ZEP; (2) A thin film layer is prepared on the first photolithography layer, wherein the material of the thin film layer is Al2O3, and the Al2O3 thin film layer is prepared by electron beam evaporation or magnetron sputtering. (3) A third photoresist is uniformly coated on the Al2O3 thin film layer to form a three-layer photoresist structure of first photoresist layer / thin film layer / third photoresist layer, wherein the third photoresist is ZEP, UVIII or PMMA. (4) Electron beam exposure and development are performed on the three-layer photoresist structure of the first photolithography layer / thin film layer / third photolithography layer. After development, the shape and position of the T-shaped gate basic structure are formed, and the developed substrate is obtained. (5) Prepare a gate metal layer on the developed substrate; (6) Remove the gate metal layer outside the shape and position of the T-type gate base structure and the remaining three-layer adhesive structure of the first photolithography layer / thin film layer / third photolithography layer after development to obtain the improved T-type gate; Al2O3 reduces the excessively rapid etching of the thin film metal during the development of the upper photoresist and inhibits the outward expansion of the etched area on both sides.

2. The method for improving the bottom edge morphology of a T-shaped grid cap according to claim 1, characterized in that, The electron beam evaporation specifically includes: forming an aluminum metal film layer by electron beam evaporation under vacuum conditions, and then introducing oxygen to form an Al2O3 thin film layer.

3. The method for improving the bottom edge morphology of a T-shaped gate cap according to claim 2, characterized in that, The magnetron sputtering method specifically includes: introducing argon and oxygen gas using magnetron sputtering to form an Al2O3 thin film layer.

4. The method for improving the bottom edge morphology of a T-shaped grid cap according to claim 1, characterized in that, In step (2), the thickness of the Al2O3 thin film layer is 0.5-100nm.

5. The method for improving the bottom edge morphology of a T-shaped grid cap according to claim 1, characterized in that, In step (4), the lower surface of the gate cap in the T-shaped gate pattern is flush with the lower surface of the thin film layer, and the lower surface of the gate foot in the T-shaped gate pattern is flush with the lower surface of the first photolithography layer.

6. A T-shaped gate prepared by the method according to any one of claims 1-5.

Images